Dark energy stands as one of the biggest mysteries in modern cosmology. Since 1998, we have known the expansion rate of the Universe is increasing, but have had no idea what is causing this acceleration. "Dark energy" is merely the name we give our ignorance. However, a new instrument called the Dark Energy Camera (DECam) may help measure many of the properties of cosmic acceleration, including whether it has always been present in the Universe, or if its effects evolved over time.

DECam on the Victor M. Blanco telescope. The camera itself is the black cylinder at the image center. Light from distant galaxies is focused by the 4-meter-diameter mirror at left into the camera.

DECam is mounted on the Victor M. Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) in Chile, where dark energy was first observed in 1998. As the name indicates, it is a camera, albeit a far more sensitive one than is available to consumers. The business end of the camera is a set of 62 charged-coupled devices (CCDs), yielding images of 570 megapixels. Unlike the CCDs present in ordinary digital cameras, those in DECam are sensitive to extremely low light levels, and it can image well into infrared wavelengths, thanks to a new detector design developed at Lawrence Berkeley National Laboratory. The largest lens on DECam is 98 cm in diameter and weighs 380 pounds (only slightly smaller than the lens on the Yerkes Observatory, which still holds the record at 102 cm).

The first images from DECam were released yesterday, and focused on many familiar astronomical objects to ensure the equipment was operating properly. Over the next 5 years, DECam will image approximately 1/8 of the entire sky as part of the Dark Energy Survey (DES), taking high-resolution pictures of roughly 300 million galaxies. The survey should discover an estimated 4000 supernova explosions, which can be used to measure the acceleration of the Universe to greater precision than ever before.

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Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population.

Combined with astrophysical information for each star, provided by on-board multi-colour photometry, these data will have the precision necessary to quantify the early formation, and subsequent dynamical, chemical and star formation evolution of the Milky Way Galaxy.

Additional scientific products include detection and orbital classification of tens of thousands of extra-solar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our Solar System, through galaxies in the nearby Universe, to some 500 000 distant quasars. It will also provide a number of stringent new tests of general relativity and cosmology.